new static water calculator By filling in the empty boxes in the water heating time calculator below and clicking the respective “Calculate!” button, you can calculate the power and/or time required to heat particular volumes of water.. Power required Specific heat capacity of water kcal/kg°C3: Volume of water to heat in litres: Starting (lower) temperature in degrees C: Finishing (higher) temperature in degrees C: Density of water in kg/dm3: Time to heat water in hours: The power required is: kW